Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

REST

The conventions most web APIs follow, with resources as nouns and methods as verbs.

A style, not a standard; resources with collection and item URLs, JSON representations, CRUD mapped to methods and status codes, stateless requests.